Field of the Invention
The present invention relates to an electro-deposited copper-alloy foil. In particular, the present invention relates to an electro-deposited copper-alloy foil suitable for a printed wiring board use.
Description of the Related Art
In recent years, a device space in a printed wiring board used for supplying an electric signal tends to be narrowed depending on high performance and downsizing of electronic and electric devices. The matter requires downsized high-density mounting on the printed wiring board. Then, a micro via-hole has been provided in the printed wiring board suitable for high density mounting to electrically conduct plural layers.
However, even when the formation of the micro via-hole in the printed wiring board should be performed by direct irradiating of a laser beam on copper foil, absorptivity of copper foil in wavelength region of an infrared laser is extremely low and it makes infrared laser working on copper foil difficult. So, the surface of copper foil should be subjected to a treatment which enhances infrared laser absorptivity.
For example, Japanese Patent Laid-Open No. 2001-226796 (hereinafter: Patent Document 1) discloses a technology to provide copper foil for laser-drilling which enables drilling by an infrared laser. Specifically, a surface layer composed of material(s) any one selected from a Sn—Cu alloy mainly composed of Sn and Cu, and metal Sn; or both the Sn—Cu alloy and the metal Sn is formed on an infrared laser radiation side surface of copper foil in copper foil for infrared laser-drilling. Furthermore, Patent Document 1 discloses a rather preferable surface layer than that consisting of just Sn; any one selected from the surface layer consisting of an alloy layer mainly composed of Sn and Cu and a metal Sn layer which is formed by subjecting a metal Sn layer formed on the surface of copper foil to a diffusion treatment to form an alloy layer mainly composed of Sn and Cu, and a surface layer consisting of an alloy layer mainly composed of Sn and Cu. As described above, Patent Document 1 discloses that the surface layer and copper foil can be subjected to infrared laser-drilling all at once when the surface layer is composed of the metal and the alloy having infrared laser absorptivity higher than that of Cu on the infrared laser radiation side surface of copper foil.
Next, Japanese Patent Laid-Open No. 2001-068816 (hereinafter: Patent Document 2) discloses a technology which improves the initial absorption efficiency of an infrared laser beam by subjecting the surface of copper foil to a black-oxide treatment. Patent Document 2 then discloses that the improvement of the initial infrared laser beam absorption efficiency on the surface of copper foil subjected to the black-oxide treatment provides an initial infrared laser-drilling shape which is uniform and flat, and it achieves excellent infrared laser-drilling.
However, in the method disclosed in Patent Document 1 subjecting the metal Sn layer formed on the surface of copper foil to the diffusion treatment to alloy Sn and Cu (that is, form the alloy layer mainly composed of Sn and Cu), composition of the alloy layer in the thickness direction will be uneven. The matter causes deviations in the etching rate along the thickness direction in the following etching process and it makes formation of a desired wiring pattern difficult.
Further, in the conventional methods disclosed in Patent Documents 1 and 2, it is difficult to reduce a manufacturing cost because the surface of copper foil should be subjected to the treatment for enhancing the infrared laser absorptivity, i.e. the methods include indispensable additional steps in a manufacturing process.
Then, an object of the present invention is to provide an electro-deposited copper-alloy foil excellent in infrared laser processability which enables uniform etching rate along a thickness direction in following etching process.